Preparation of limonene



Patented Aug. 14, 1945 I I UNITED STATES PATENT OFFICE PREPARATION OF LIMONENE Morris S. Kharasch, Chicago, 111., and William Bryan Reynolds, Cincinnati, Ohio, assignors to Research Corporation, New York, N. Y., a corporation of New York No Drawing. Application August 21, 1944, Serial 110,550,486 8 Claims. (Ql.-g6 0675.5) This invention relates to the preparation 01 amide of a diflerent acid. Examples of amides limonene from pinene and more particularly to a hich can be used are, formamide, acetamide, process for preparing limonene by heating pinene benzamide and salicilamide. ,In. addition, certain with an organic acid in the presence of an organic agents can be used which form amides by reacting acid amide, ';;'With the acid used as isomerization catalyst. It is'well known that pinene, when heated v, ,Such agents are exemplified by ammonia and with organic acids, is converted into esters 01'.. v urea. borneol. As by-products of such conversion In carrying out the process of the present insmall quantities of active limonene are produced. e t n. p e is t d at temperatures e i However, yields are never large since acids which 10 120 to 200 C. with an organic acid and -,.an cause limonene to be produced are readily ester-l organic acid amide for a period iv-time. vary fied by the pinene, such esters forming the prining from a few to as much vas fi ftyhours, siccipal products of the reaction. P di po the reagents and temperature When optically active pinene is heated to temchosen. The reaction mixture is steam dis peratures above 200 C., it isomerizes thermally to tilled to obtain the tcrpene; which may; (3311- F produce dl-limonene, commonly known as ditain as much as seventy or eighty per cent pentene. A satisfactory process for the producactive limonene plus a little unreacted p nene and tion of limonene from pinene should therefore a small amount of by-product: The pure take place at temperatures below 200 C. limonene is obtained byfractionating' the crude The invention has a an objectthe preparation terpene. The residue from thefsteam distillaf f" of dor l-iimonene, in good yield, from the cortion is made alkaline with caustic and heat to A responding dor l-alpha or beta pinene. A fur-'- hydrolyze the amide. After clarification of "the ther object is the catalytic isomerization of solution, the acid is recov d in'good'yi ld'i y pinene to limonene by organic acids under condicidifying the solution and filtering ofi thel retions largely preventing the esterification 01' the. cipitated acid. acids. The invention is further illustrated by the fol'-. These objects are accomplished by heating lowing examples: pinene with organic acids in the presence of organic acid amides at temperatures below 200 C. Emmple 1 When pinene is heated with organic acids, 30 esters of borneol are obtained. Yields of esters obtained depend upon the temperature and the particular acid used. Weak organic acids such as acetic and benzoie give poor yields of esters when temperatures of the order of 140 C. are used. However, higher yields are obtained at temperatures of 175 to 200 C. When somewhat a stronger organic acids such as chloroacetic acid, d'hmonenei 174-73 73, d4 0.841,

m-nitro benzoic, benzoylbenzoic, and salicylic are Observed 1 tube The used, the yields of ester obtained at 140 C. are 40 benzoylbenzom acld 1S recovered by heating the quite good. The same acids and conditions which residue from the steam distillation with caustic, bring about good yields of ester are also effective clarifymg h solutiqn and precipitatting the acid in catalytically converting pinene to limonene. by the addition of mmeral acid Acld recovery 15 d-alpha-pinene, 136 parts (one mole), is heated with benzoylbenzoic acid, 113 parts (0.5 mole), and formamide, 18 parts (0.4 mole) for forty hours at 1401-2" C. The reaction mixture is 35 steam distilled to recover 128 grams of terpene. Fractionation of the crude terpene yields 20 grams of unreacted pinene and 95 grams of However, limonene cannot be commercially pregoodpared by such a process since the yields are low. Example 2 In the present invention it has been discovered that the esterification of the acids by pinene can d-alDha-p ne e, One mole, is heated with be inhibited without materially inhibiting the s licyli a id, mole, a am d 0- 8 m l capacity of the acids to isomeriz the pinene to for forty hours at 150:? C. The reaction mixlimonene. Agents which will thus inhibit the ture is worked up as described-in Example 1. The esterification reaction are quite specific and, for amount of unreacted pinene in this example was practical purposes, are limited to the class com- 469 g ams, while 50 g ams of d-limonene were prising organic acid amides. The organic acid bbtained. In addition, three grams of borneol amide used may be the amide of the same acid were obtained after saponification of the residue used as isomerization catalyst or it m y be an filistrom the steam distillation.

Example 3 Example 4 d-alpha-pinene,. one mole, is heated with benzoylbenzoic acid, 0.4 mole, and urea 0.15 mole,

for forty hours at 140:2" C. The reaction mixture is worked up and limonene recovered by the method described in the previous examples. The yield of limonene is 50% of theory.

Example 5 Same as Example 1, except that beta-pinene is used in place of alpha-pinene. limonene is comparable.

Example 6 Same in Example 1, except thatl-alpha-pinene is used in place of d-alpha-pinene. In this example, 'l-limonene is 'formedas the principal product of the reaction.

Example 7 Same as Example '2, except that monochloroacetic acid, oi z'mole, is used in place of salicylic acid. The yield of d-limonene is somewhat better than in Example 2.

The term pinene has been used in this specification to include all members of the class. l-alphapinene,

comprising d-alpha-pin'ene, 'd-betapinene, and l-betapinene, As, starting material for the preparation of d-limonene, d-alphapinene and d-be'tapinene are equivalent and as starting material for the preparation ,oi

The yield of into the hot reaction mixture.

' ing amide; 1.5

compound of the type R/COOH where R is an organic radical. Diand polybasic acids are also included. The term organic acid amide" includes any compound of the type R-CQNHz where R- is an organic radical. Such an amide is preferably preformed and added to the reaction mixture. However, an equivalent procedure' is to add some reagent to the reaction mixture, which will produce organic acid amides in situ. For example, ammonia may be passed In either instance, a part of the acid used for the catalytic isomerization is converted into the correspond- The term in the presence of an organicacid amide therefore includes both the addition of the preformed amide or the formation of the amide in the reaction mixture.

; We claim:

l-limonene, l-alpha-pinene and l-betapinene are equivalent. The isomerization of pinene to limonene is a proton catalyired reaction and the r 1. The process for the production of limonene which comprises heating pinene with an organic acid in the presence of an organic acid amide.

2. The process for the production of limonene which comprises heating pinene at a tempera,- ture of from 120 C. to 200 C. with an organic acidin the presence of an organic acid amide. 3. The process for the production of d-limonene which comprises heating a substance of the group consisting of d-alpha-pinene and d-beta-pinene with an organic acid in the which comprises heating pinene with benzoyl-' benzoic acid in the presence of an aliphatic acid amide. I

7. The process'forthe production of limonene which comprises heating pinene with salicylic acidin the presence of an aliphatic acid amide. 8. The process for the production of limonene which comprises heating pinene with chloroaceticacid in the presence of an aliphatic acid amide.

MORRIS S. KHARASCH. WILLIAM BRYAN REYNOLDS. 

